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Hot runner technology in two-color injection mold
Jul 10, 2018

First, two-color mold

The two plastic materials are injection molded on the same injection molding machine and molded in two parts, but the product is only molded once. Generally, this molding process is also called double-material injection molding, usually completed by a set of molds, and requires a special two-color injection molding machine.

Two-color molds are becoming more and more popular on the market today. This process can make the appearance of the product more beautiful, easy to change colors and can be sprayed, but it is expensive and technically demanding.

In the manufacture of a two-color mold, a hot runner is sometimes used, and the hot runner mold is a mold that uses a heating device to keep the melt in the runner from solidifying at all times. Because it is shorter than the traditional mold forming cycle and saves raw materials, hot runner molds are widely used in various industrialized countries and regions in the world today.

The hot runner system is composed of three parts: hot nozzle, runner plate and temperature control box. It is a perfect form of plastic injection in plastic injection molding. The working principle of the hot runner system is: installing a heater in a plastic mold, using the principle of heating and temperature control to keep the runner of the mold in a molten state, just as the nozzle of the injection molding machine directly extends to the feeding point of the product cavity, so that the product is more Direct and easy molding.


Second, the performance of the hot runner

(1) precisely control the temperature of the melt plastic to eliminate material degradation;

(2) Balanced flow channel design, the part cavity is evenly filled;

(3) There is no dead zone in the flow channel to ensure rapid color change and prevent material degradation to minimize pressure loss.

The choice of hot runners. Many conditions are factors to consider when selecting a hot nozzle, such as different plastic properties, shape, size, thickness, weight, cavity arrangement, and gate location. There are several types of hot nozzles and runner plates of different shapes and sizes to suit a variety of products.

Conventional injection molding often has the following disadvantages:

1. It is difficult to fill the mold;

2. Deformation of thin-walled large parts;

3. Waste of the runner material;

4. The quality of injection molded parts of multi-cavity molds varies.


Third, the advantages of hot runners

1. Save raw materials and reduce costs;

2. Shorten the molding cycle and improve machine efficiency;

3. Improve the surface quality and mechanical properties of the product;

4. It is not necessary to use a three-plate mold to use a point gate;

5. It is economical to form a single product with a side gate;

6. Improve the degree of automation;

7. The gate can be controlled by a needle valve gate;

8. The quality of the injection molded parts of the multi-cavity mold is consistent;

9. Improve the surface appearance of injection molded products.


Fourth, the disadvantages of hot runners

1. The mold structure is complex, the cost is high, and the maintenance cost is high;

2. It takes a while for the boot to be stable, resulting in more waste.

3. When there is melt leakage and heating element failure, it has a great influence on product quality and production schedule.

The third shortcoming of the above is particularly important, because the hot runner mold operation and maintenance is complicated compared with the cold runner mold. If the operation is improper, it is easy to damage the hot runner parts, making the production impossible, resulting in huge economic losses. For new users of hot runner molds, it takes a long time to accumulate experience. These disadvantages can be reduced by purchasing quality heating elements, hot runner plates, and nozzles that are carefully maintained during use.

Fifth, Several situations in which a hot runner system is required

1. Injection molding products with strict quality requirements;

2. A variety of plastic, multi-color co-injection process;

3. The gate direction is at a certain or perpendicular angle to the mold opening direction;

4. Multi-layer mold, a way to increase the output without increasing the tonnage of the injection molding machine is to use a multi-layer mold, that is, there are a plurality of parting surfaces on the mold, which is completely realized by the hot runner system;

5. The gate is opened on the inside of the deep part. Some industrial products are extremely strict in appearance. When using it, no trace of the gate is allowed to be exposed. Small such parts such as makeup lipstick caps and car interior parts. At this point you need to open the gate inside the part. When the depth of the part is too large, it is impossible to use the cold runner gate, but only the hot runner nozzle can be used to form the inside of the part for injection molding.

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